function z = kowa(x)
%Kowalik and Osborne function
%n=4,m=11,x0=[0.25,0.39,0.415,0.39]
%fmin1=f15([inf;-14.07;-inf;-inf])=1.02734*10^(-3) 
%Author:Ji Lin
y=[0.1957,0.1947,0.1735,0.1600,0.0844,0.0627,0.0456,0.0342,0.0323,0.0235,0.0246];
u=[4,2,1,0.5,0.25,0.167,0.125,0.1,0.0833,0.0714,0.0625];
z=ones(1,11);
for ii=1:11
    z(ii)=y(ii)-x(1)*(u(ii)^2+u(ii)*x(2))/(u(ii)^2+u(ii)*x(3)+x(4));
end
z=sum(z.^2);